Light pollution (also known as photo-pollution or luminous pollution) refers to light that is annoying, wasteful or harmful. Like other forms of pollution (e.g., air pollution, noise pollution, water pollution, soil contamination), light pollution can harm the environment and human and animal health.
Light pollution is a broad term that refers to multiple problems, which are caused by inefficient, annoying or arguably unnecessary use of artificial light. Specific categories of light pollution include light trespass, over-illumination, glare, clutter, and sky glow. Often annoying or wasteful light fits several of these categories.
Light trespass occurs when unwanted light enters one's property, for instance, by shining light over a neighbor's fence. Often, light trespass occurs when strong light enters through the window of one's home. The strong light may cause problems such as sleep deprivation or the blocking of an evening view.
Light is particularly problematic for astronomers. Stray light may limit an astronomer's ability to observe the night sky. For this reason, most major optical astronomical observatories are surrounded by zones of strictly-enforced restrictions on light emissions.
A number of cities in the United States have developed standards for outdoor lighting to protect the rights of its citizens. The International Dark-Sky Association has developed a set of model lighting ordinances. U.S. federal agencies also promulgate and enforce standards and process complaints within their areas of jurisdiction. For instance, the FAA promulgates and enforces lighting requirements for white strobe lights on communication towers. The FCC maintains a database of Antenna Structure Registration information, which citizens may use to identify offending structures. The FCC also provides a mechanism for processing consumer inquiries and complaints.
The U.S. consumes energy that is equivalent to 50 million barrels per day of petroleum. The U.S. Department of Energy notes that 60% of that energy comes from nuclear power, natural gas, hydroelectric and other non-petroleum sources. The U.S. Department of Energy further notes that over 30% of all energy consumed in the U.S. is consumed by commercial, industrial, and residential sectors. Energy audits of existing buildings demonstrate that lights in residential, commercial, and industrial buildings consume about 20 to 40% of all energy consumed in the U.S. Thus, lighting energy accounts for the equivalent of about four or five million barrels of oil per day. Energy audit data demonstrates that about 30 to 60% of energy consumed in lighting is unneeded or gratuitous. Indeed, over-illumination (i.e., the excessive use of light) wastes energy equivalent to two million barrels of petroleum per day.